The objective of this study is to evaluate the biologic basis of adaptations that occur after superior surgical impaction of the maxilla in Macaca irus monkeys. A total of seventy-eight monkeys, forty-eight experimental and thirty control will be used. The animals will be sacrificied 1 week, 2 weeks, 1 month, 3 months, 6 months, 12 months and 18 months after surgery. The biologic changes that will be studied are, the nature of union and revascularization at the surgery site; sutural, osseous and cartilagenous remodelling of the midfacial bones and mandible; and adaptation of the muscles of mastication, muscle-born interface, dentition and pulp. The study will also use growing monkeys to determine the effect of surgery on short- and long-term growth and development of the face. The above mentioned parameters will be studied with the help of osseous and muscle implants, vital staining, cephalometry, stereophotogrammetry, radioactive istopes and carefully executed biomechanical, biochemical and histologic techniques.